Lateralus emerged after a four-year legal dispute with Tool's label, Volcano Entertainment.[6] In January 2001, the band announced that their new album's title would be Systema Encéphale and provided a 12-song track list with titles such as "Riverchrist", "Numbereft", "Encephatalis", "Musick", and "Coeliacus". File-sharing networks such as Napster were flooded with bogus files bearing the titles' names.[7] At the time, Tool members were outspokenly critical of file-sharing networks in general due to the negative impact on artists that are dependent on success in record sales to continue their career. Keenan had this to say during an interview with NY Rock in 2000: "I think there are a lot of other industries out there that might deserve being destroyed. The ones who get hurt by MP3s are not so much companies or the business, but the artists, people who are trying to write songs."[8] A month later, the band revealed that the new album was actually titled Lateralus (supposedly a portmanteau of the leg muscle Vastus lateralis and the term lateral thinking)[9] and that the name Systema Encéphale and the track list had been a ruse.[10]

Lateralus and the corresponding tours would take Tool a step further toward art-rock,[11][12][13]math rock, and progressive rock[1][14][15] territory, in contrast to the band's earlier material, which has often been labeled as alternative metal.[16]Rolling Stone wrote in an attempt to summarize the album that "Drums, bass and guitars move in jarring cycles of hyperhowl and near-silent death march... The prolonged running times of most of Lateralus' thirteen tracks are misleading; the entire album rolls and stomps with suitelike purpose."[1] Joshua Klein of The A.V. Club in turn expressed his opinion that Lateralus, with its 79-minute running time and relatively complex and long songs — topped by the ten-and-a-half minute music video for "Parabola" — posed a challenge to fans and music programming alike.[17] Drummer Danny Carey said, "The manufacturer would only guarantee us up to 79 minutes... We thought we'd give them two seconds of breathing room."[18] Carey aspired to create longer songs like those by artists he grew up listening to. The band had segues to place between songs, but had to cut out a lot during the mastering phase.[18] The CD itself was mastered using HDCD technology.

Just as Salival was initially released with several errors on the track listing, early pressings of Lateralus had the ninth track incorrectly spelled as "Lateralis".[6] The original title of "Reflection" was "Resolution" before being changed three months prior to the album's release.[7]

The track listing is altered on the vinyl edition, with "Disposition" appearing at track 8. Because of the long running time, the double vinyl edition could not be released like the disc since the songs would not fit on each disc side in that order. By moving "Disposition" to an earlier point, the sides were balanced and could fit the material. However, this edit breaks the segue that occurs between "Disposition" and "Reflection" which, along with "Triad", are often grouped together.

The insert is translucent and flips open to reveal the different layers of the human body. Disguised in the brain matter on the final layer is the word "God". The artwork was done by artist Alex Grey, who would later design the 3D edition cover for the followup to Lateralus, 10,000 Days.

The title track, "Lateralus", incorporates the Fibonacci sequence.[22] The theme of the song describes the desire of humans to explore and to expand for more knowledge and a deeper understanding of everything. The lyrics "spiral out", refers to this desire and also to the Fibonacci spiral, which is formed by creating and arranging squares for each number in the sequence's 1,1,2,3,5,8,... pattern, and drawing a curve that connects to two corners of each square. This would, allowed to continue onwards, theoretically create a never-ending and infinitely-expanding spiral. Related to this, the song's main theme features successive time signatures 9/8, 8/8, and 7/8.[23] The number 987 is the sixteenth integer of the Fibonacci sequence.[24]

A vinyl edition and two DVD singles from the album were released later. The "double vinyl four-picture disc" edition of Lateralus was first released as a limited autographed edition exclusively available to fan club members and publicly released on August 23, 2005. Two music videos were produced; one for "Schism" (with the short ambient segue "Mantra" at the beginning) and one for "Parabol/Parabola". These were subsequently released as two separate DVD singles on December 20, 2005, featuring remixes of the tracks by Lustmord.

Overall, Lateralus was critically well received and its complexity provoked many responses akin to what Ryan Rayhil of Spin magazine had to say about the album, calling it a "monolithic puzzlebox".[37]Q listed Lateralus as one of the best 50 albums of 2001.[38] The album was ranked number 32 on Rolling Stone's 50 Greatest Prog Rock Albums of All Time list.[39]

Well received by both fans and most critics, it was named Kerrang!'s album of the year in 2001, and the band received the 2002 Grammy Award for Best Metal Performance for the song "Schism".[40] During the band's acceptance speech, drummer Danny Carey stated that he would like to thank his parents "for putting up with [him]", and bassist Justin Chancellor concluded, "I want to thank my dad for doing my mom."[41]Kludge ranked Lateralus at number two on their list of top 10 albums of 2001.[42] In 2016, Loudwire named Lateralus the #1 hard rock/metal album of the 21st century.[43]

NutSie.com ranks the drumming performance by Danny Carey on the song "Ticks & Leeches" number three on their list of Top 100 Rock Drum Performances.[44]

The album was a commercial success in the United States, debuting at No. 1 on the U.S. Billboard 200 albums chart with over 555,200 copies sold in its first week of release.[3] On August 5, 2003, the album was certified double platinum by the RIAA. On August 30, 2004, the album was certified silver by the BPI for sales of 60,000 in the U.K.[45] In addition, Lateralus was certified platinum by the ARIA[46] and double platinum by MC.[47]

Lateralus sold 555,000 copies in its first week, debuting at number one on the Billboard 200.[48] As of July 7, 2010, Lateralus has sold 2,609,000 copies in the US. It is ranked number 123 on the Rock and Roll Hall of Fame's "Definitive 200" list.[49]

^ abKen Micallef (June 2001). "Danny Carey: Demon On Drums". Modern Drummer, transcribed by Ruskin F. for The Tool Page. Retrieved 17 April 2007. I also had a piano that was destroyed. I got some good samples from that, banging on the strings for 'Resolution.'